get one of those roll on deoderant containers and a screwdriver, put the screw driver in between the ball and the outside and move it around the the ball and then pop the ball out. empty out what ever's in there and use a hair dryer or a cloth to dry the inside. pull off a stirp of felt froma chalk board earaser and make sure it fits nicely in the top. fill the container with your choice of ink and put the earaser nib on. put it against an upright surface and squeeze lightly untill the nib becomes nice and juice with ink. go and destroy shit!

try some thicker ink maybe or maybe try putting some seranrap or how ever its spealt heavily around the screw off thing, then surround it with tape....sounds like a retarted idea hahah..or just try other shit over then seran rap if it doesnt help. you should just consider getting another marker..molotow burners r real good and dont leak..theres other good markers out tehre too though obviously

double ended glue marker/pen you can get them at target or walmart empty it and rinse it out fill it with 3/4 paint and 1/4 peroxide works great and is usally a household item and cheaper than paint thinner

liquid paper correction pen/any other white out pen works great (for the most part)
Yes, they are not very permanent. But they are great little things just to have in your pockets.
You can get a nice discount at most places that carry them too.

get one of those smaller waterbottles (they usually make them for kids) they're perfect for one hand, easy to control. all you have to do is fill it up, plug the tip with felt, and screw the lid back on for travel. they can get messy if you squeeze too hard, so be careful.

I found this out today if you have a broad line deco that is streaking or seems to be dry then pull out the nib turn it over (dont worry no paint will come out) then put the nib back in and push it down a few times and it should be good again.